The invention relates to cellular plastic materials.
There are several classes of thermosetting resin system that could be considered as possible candidate materials for the production of fire resistant low-density cellular insulation foam when compounded with appropriate additives. However, the required flammability performance restricts selection of many types of organic thermosetting resin. For instance, halogen atoms would need to be incorporated into the chemical backbone of unsaturated polyester resins and epoxy resins to impart self-extinguishing behaviour. Alternatively, unsaturated polyester resins and epoxy resins would need to be blended with halogenated compounds to impart self-extinguishing behaviour. Such chemical compositions would generate toxic gases such as hydrogen chloride or hydrogen bromide in a fire situation. Addition of other types of non-halogenated flame-retardant such as organo-phosphorous compounds can give rise to high smoke emission in a fire situation. The addition of a flame-retardant compound may also have an adverse effect on cellular plastic mechanical strength. Other, thermosetting resins such as polyurethane and polyisocyanurate resins produce high smoke and toxic gas emissions in a fire situation Polyurethane may not be self-extinguishing in a fire situation. Hence these materials cannot be the materials of choice if fire performance is a concern.
Historically, phenolic resins have been the preferred thermosetting plastic material when low smoke emission and self-extinguishing ability are of paramount importance in a particular application.
Presently, in cellular foam manufacture, a phenolic resole resin is commonly catalysed by either a strong organic or inorganic acid. For example DE3329334 A describes a process for the production of an acid cured phenol resin foam in which the acids are premixed with novalak resin before addition of a phenolic resole. The selection of acid type is dependent on the desired curing time and temperature. Cellular insulation foam is produced when the blowing agent that has been pre-blended into the resin, starts to boil. Halocarbons are commonly used blowing agents. Expansion typically occurs in the temperature range 25xc2x0 C. to 80xc2x0 C. In thick sections of acid cured phenolic foam, it is possible that a resin exotherm will develop. The occurrence of an uncontrolled exothermic chemical reaction is more likely when a strong acid is used as catalyst. When exothermic reactions develop, large amounts of water or steam are created by the phenolic resins condensation polymerisation reaction. The consequential shrinkage of the resin matrix can adversely affect the ability to form a closed cell foam structure as well as impairing the mechanical strength performance. Closed cell foam structure is highly desirable to maximise insulation performance.
As conventional phenolic foam is produced using an acid catalyst, there has been concern that when this foam is in direct contact with metal, such as an insulated pipe, it could induce corrosion of the metal. Hence there is a desire for a foam insulation product that has the mechanical strength and fire performance of an acid catalysed phenolic foam, yet is pH neutral or moderately basic. Such a material would alleviate the risk of induced acidic corrosion.
EP-A-0166275 describes a resin composition for a molding material used particularly for electrically insulating laminated plates. The resin comprises a resole phenolic resin, an epoxy resin and a strength enhancing amine compound.
It is well known that alkaline phenol formaldehyde resole resins can be cured by aliphatic esters to produce a chemical binder for foundry sand moulds and cores as described in JP-A-130627/1975 and EP-A-O 085 512. Also, U.S. Pat. No. 3,599,433 and U.S. Pat. No. 3,696,622 discuss alkaline phenol formaldehyde resole resins reacting with a lactone as a method for soil stabilisation and leakage prevention. It has been documented in EP-A-0146499, JP-A-S62-250267, JP-A-04364908 and JP 01092242A that acid free phenolic cellular plastic can be produced by curing an alkaline phenol formaldehyde resin with various aliphatic esters.
Other commercial applications using alkaline phenol formaldehyde resins cured by aliphatic esters such as lactones have been limited due to the inherent high shrinkage of the cured phenolic resin.
There is a need for a stable cellular plastic foam that has good mechanical strength and fire performance.
According to the invention there is provided a resin mixture for forming a cellular plastic foam, the resin mixture containing a phenolic resole, a chain extending agent, and as curing agents, a base, and an ester and/or an aliphatic carbonate.
In one embodiment the chain-extending agent is an epoxy resin.
In another embodiment the chain-extending agent is a thermoplastic modifier.
In a particularly preferred embodiment the chain extending agent includes an epoxy resin and a thermoplastic modifier.
Preferably the thermoplastic modifier is a phenolic novalak resin.
Preferably the phenolic novalak has a number average molecular weight between 1000 and 1500.
Preferably the phenolic novalak is present in an amount from 2% to 30% by weight. Most preferably in an amount from 14 to 25% by weight.
In one embodiment of the invention the resin mixture has a pH of at least 9.
In one embodiment the epoxy is present in an amount from 2% to 30% by weight.
Preferably the epoxy resin contains at least two epoxy groups in the molecule.
The epoxy is preferably based on oligomers of diglycidylether of Bisphenol A or diglycidylether of Bisphenol F or mixtures thereof.
Preferably the phenolic resole has a reactive solids content in the range of from 50% to 85% by weight.
In one embodiment the phenolic resole is prepared from an optionally substituted phenol and an aldehyde in the molar ratio of phenol to aldehyde of 1:1 to 1:3.0
Typically the base is potassium hydroxide and/or sodium hydroxide.
Preferably the ester is a lactone. Ideally the ester is selected from one or more of xcex3-butyrolactone and caprolactone.
Preferably the ester is present in an amount of from 2 to 25% by weight.
In one embodiment the resin mixture includes a blowing agent. The blowing agent may be a liquid and/or a gas.
Preferably the blowing agent has a boiling point of up to 70xc2x0 C.
In a preferred embodiment the blowing agent is present in the resin mixture in an amount of up to 25% by weight.
Preferably the blowing agent is a halogenated hydrocarbon, especially pentafluorobutane and/or 1,2 dichloro-1-fluoroethane and/or pentane or mixtures thereof.
In one embodiment the resin mixture includes a surfactant, especially a non-ionic surfactant.
The surfactant may be a dimethylsiloxane/polyoxyalkylene copolymer.
Preferably the surfactant is present in an amount of from 1 to 15% by weight. The invention also provides a process for the preparation of a cellular plastic by expanding and curing a resin mixture of the invention.
In one embodiment the cellular plastic is manufactured at atmospheric pressure.
Alternatively the cellular plastic is manufactured at a pressure less than atmospheric pressure.
In another embodiment the cellular plastic is manufactured at a pressure greater than atmospheric pressure.
The invention further provides a cellular plastic whenever manufactured using a resin mixture of the invention and/or using a process of the invention.
Preferably the cellular plastic has a thermal conductivity of less than 0.04 W/mK, most preferably less than 0.025 W/mK.
Preferably the cellular plastic for insulation has a substantially closed cell structure, ideally having a closed cell content of greater than 90%. Most preferably this closed cell structure is stable over an extended period of time at room temperature.
The materials described herein relate to formulated phenolic resin compositions. These compositions can be used to manufacture closed cell insulation foam that is self-extinguishing in a fire situation. Also this cellular insulation foam generates low smoke emission. The cellular insulation foam material described herein satisfies the mechanical strength criteria and non-burning specification requirements for use in various insulation applications. The thermal and sound insulation of buildings and transport are areas of application for such products as are the lagging of pipe sections.
The cellular insulation foam materials of the present invention can be manufactured at temperatures between 10xc2x0 C. and 90xc2x0 C. under either atmospheric pressure or partial vacuum.
The present invention relates to fire resistant cellular foam insulation produced from a two part acid free modified Phenolic resin system. This resin system cures with minimal shrinkage and has a high proportion of closed foam cells. Open cell foams may also be produced in this way however closed cell foams maximise thermal insulation performance as measured by thermal conductivity. Thermal conductivity is tested by BS 4370. The chemical composition of the resin system for foam manufacture of the present invention comprises the following. An alkaline phenol formaldehyde resole resin, an aliphatic ester and/or aliphatic carbonate, a blowing agent and surfactant. Chain-extending agents such as thermoplastic phenolic novalak resin and/or epoxy resin are also key components of the present chemical composition. In particular enhanced insulation performance was achieved by creating a stable closed cell foam.
The presence of thermoplastic phenolic novalak resins in the chemical composition could also serve to enhance the toughness of the cured phenolic foam. The phenolic novalak resin selected may be pre-dissolved or pre-dispersed to a limited degree as a micronised powder in either the uncured alkaline phenolic resole resin, the epoxy resin or in the aliphatic ester/aliphatic carbonate.
The epoxy resin selected can be pre-dissolved in phenolic resole resin, aliphatic ester/aliphatic carbonate, blowing agent or combinations thereof.
A feature of the invention is that the phenolic novalak used can react with both the epoxy resin and the phenolic resole to create a complex cured phenolic-epoxy copolymer. In the chemical composition on which the invention is based, a catalyst such as triphenyl phosphine, (TPP), is optionally included in appropriate proportions to promote the chemical reaction between phenolic novalak and epoxy resin at 30-80xc2x0 C. It is believed that the presence of an alkali such as potassium hydroxide, plus an aliphatic ester such as caprolactone or butyrolactone will promote polymerisation of the phenolic resole resin. When phenolic novalak is also present in the said chemical composition, the alkali and aliphatic ester will also assist in promoting a chemical reaction between phenolic resole and phenolic novalak. When caprolactone is selected as the ester in the chemical composition, it is believed that the presence of an alkali could also promote formation of polycaprolactone as a side reaction. The presence of polycaprolactone will act as a toughening agent enabling the cellular plastic to be less brittle.
The inclusion of a controlled amount of epoxy resin does not significantly detract from the favourable fire performance associated with phenolic resins alone. It is also possible to include in the chemical composition of the invention the option of a catalyst that will promote only epoxy homopolymerisation. For instance 2-ethyl 4-methyl imidazole. Such a catalyst can be used to optimise insulation foam manufacturing time. It may also ensure that no unreacted epoxy chemical groups remain.
The material system of the present invention can also optionally comprise appropriate additives. For instance, flame retardants, fillers, reinforcing materials, coupling agents, pH adjusting agents, elastomeric or thermoplastic toughening agents, plasticisers and dyes. These additives serve to optimise either or both the uncured and the cured physical properties of the material composition.
Blowing agents can include but are not limited to fluorinated and or chlorinated hydrocarbons, alcohols, ketones and alkanes. Preferred, are blowing agents such as pentafluorobutane and 1,2 dichloro-1 1 fluoroethane and pentane. To the chemical composition, which is the basis of the invention, is added up to 25% by weight of blowing agent, more typical is the range 2 to 10% by weight to achieve the desired foam density. (15-125 kg/m3). The amount of blowing agent can be varied to suit the desired final density of the cellular insulation foam.
For cellular insulation foam manufacture, surfactants are also present in the chemical composition. Non-ionic siloxane-oxyalkylene, oxyalkylated castor oil and polyoxyalkylated alkyl phenols have been used successfully as surfactants both individually and in combination. For the chemical composition which is the basis of the invention it is preferred that between 1 and 15% surfactant is employed. More preferable is the range 2 to 6% by weight.
EP-A-0146499 describes examples of suitable phenolic resole type resins that can also be used in the present invention. These also include but are not restricted to phenolic resole resins based on substituted phenols such as m cresol, 3,5-xylenol resorcinol and mixtures thereof.
It has been found that the selection of a resole with higher molecular weight can improve mechanical strength of the final cellular insulation foam produced.
A phenolic resole resin with a percentage cured reaction solids of 60-85%, and more preferably 70-80% solids, is mixed with an alkali such as potassium hydroxide to give a hydroxyl anion content in the range 0.5%-10% more preferably 1%-3.5%. Therefore in the total composition of the present invention, it is possible for up to 60% by weight of phenolic resole to be employed. More preferably the total phenolic resole content is 25 to 45% by weight.
Phenolic resole solids content is determined using a 4 g sample of phenolic resole resin, subjecting it to 140xc2x0 C. for one hour and recording residual weight. Hydroxyl anion content can be determined by titration with a molar standard solution of dilute acid.
EP-A-0146499 describes examples of aliphatic esters and aliphatic carbonates that can be used in the present invention. These include, but are not restricted to, xcex3 butyrolactone, caprolactone, valerolactone, propiolactone, glycerol triacetate, glycerol diacetate, glycerol monoacetate, methyl formate, ethyl formate and ethylene glycol diacetate, ethylene carbonate, and propylene carbonate. Most preferred are xcex3 butyrolactone and caprolactone. These organic esters can be used individually or in combination to regulate reactivity. For the chemical composition which is the basis of the invention it is preferred that between 2 and 25% by weight ester is employed. More preferable is the range 6 to 13% by weight.
Commercially available phenolic novalak resins are part of the chemical composition that is the basis of the current invention. Phenolic novalak resins are thermoplastic materials whose aromatic rings can be linked in either the ortho, meta or para ring positions. For use in the present invention, the phenolic novalak selected should have a number average molecular weight of 1000-1500.
Similarly ortho, meta or para novalak phenolic resins with pendant chemical substituents such as cresols, can also be considered to be within the scope of the present invention. Similarly ortho, meta or para linked novalak phenolic resins modified by nitrile rubber can also be considered to be within the scope of the present invention. Phenolic novalak resins based on aldehydes other than formaldehyde, such as furfural, can also be considered to be within the scope of the present invention. For the chemical composition which is the basis of the invention it is preferred that between 2 and 30% by weight phenolic novalak is employed. More preferable is the range 14 to 25% by weight.
Before combining an alkaline phenol formaldehyde resole type resin with a suitable aliphatic ester, it is preferable to predissolve some or all of the modifying phenolic novalak in either the alkaline phenol formaldehyde resole resin or the aliphatic ester. Generally it is preferred that the aliphatic ester selected can predissolve some or all the required amount of phenolic novalak.
Commercially available epoxy resins are part of the chemical composition that is the basis of the current invention. The epoxide compounds which can be used herein include but are not limited to epoxy resins obtained by reacting Bisphenol A, tetrabromobisphenol A, Bisphenol F, resorcinol, phenolic novalak, methylene dianiline, para amino phenol or polyalkylene glycol with epichlorohydrin. Particularly favoured are commercially available liquid epoxy resins Epikote 862 and 828 from the Shell Company. For the chemical composition which is the basis of the invention it is preferred that between 2 and 30% epoxy resin is employed. More preferable is the range 10 to 20% by weight.
As well as conventionally manufacturing cellular insulation foam in the temperature range 40-90xc2x0 C. depending on the selected blowing agent and resin reactivity, it is a feature of the invention that foam can be manufactured under reduced pressure at ambient temperature. When an appropriate vacuum is applied, the blowing agent will begin to boil. After the resin system has cured sufficiently, the vacuum is removed leaving cellular insulation foam. (Example 4 describes such a procedure). Using a vacuum manufacturing method for cellular foam manufacture is not easily achievable with strong acid catalysed phenolic foam, as the exothermic chemical reaction cannot be readily controlled particularly in large sections. It will also be appreciated that cellular foam could be manufactured by introducing gas under pressure, into the combined 2 part resin system at an appropriate temperature, for instance, carbon dioxide.
Procedures for applying the material compositions of the invention to the manufacture of low-density cellular foam are described below. The chemical compositions on which the invention is based are two-part resin systems of modified phenolic resin that have been cured by base and ester. The mixing of chemical components described herein to produce foam is achieved by using either a standard mechanical mixing head, a static mixer, or by high pressure impingement mixing of two component streams. All these mixing techniques are well known in polyurethane or phenolic foam manufacture.
The chemical compositions can be cured at temperatures between 10 and 90xc2x0 C. under atmospheric pressure, most preferably, between 50 and 70xc2x0 C. under atmospheric pressure. Alternatively, the chemical compositions on which the invention is based can also be adapted to cure under partial vacuum between 15 and 50xc2x0 C. Most preferably between 18 and 35xc2x0 C. The insulation foam produced by either manufacturing technique is non acidic.
Example 1 describes a chemical composition on which the invention is based. By comparing Examples 1 and 2, it is demonstrated that insulation foam based on a novalak modified epoxy-phenolic copolymer that has been cured by an alkali and an ester, has a stable lower thermal conductivity compared to phenolic resole cellular foam cured by alkali and ester without such epoxy and novalak modification. Similarly, the former cellular foam demonstrates much higher compressive strength over the latter.
If an alternative fire resistant thermoplastic such as polyethersulphone, (PES), is selected in place of phenolic novalak, inferior insulation performance is observed. This may be due to the fact that PES probably does not chemically react into the polymer backbone in the typical temperature range used to manufacture insulation foam. By comparing Examples 1 and 3, it is demonstrated that insulation foam based on a novalak modified epoxy-phenolic copolymer that has been cured by base and ester, has a stable lower thermal conductivity value compared to an epoxy-phenolic cellular foam cured by base and ester and modified by PES.
Example 4 describes the preparation of a novalak modified epoxy-phenolic copolymer at 20xc2x0 C. under vacuum.
Cellular foam based on the chemical composition of the present invention maintains the fire self extinguishing and low smoke behaviour associated with conventional acid cured phenolic insulation foam.